1. Field of the Invention
The present general inventive concept relates to a developing device, and more particularly, to a liquid developing device using a liquid developing agent having a high concentration.
2. Description of the Related Art
A liquid developing agent is a developing agent in which powdery toner particles are dispersed into a liquid carrier (solvent). Hereinafter, the liquid developing agent is referred to as ink. A liquid developing device is a device which develops an electrostatic latent image formed on a photosensitive body by supplying the ink to the electrostatic latent image.
FIG. 1 shows an example of the structure of a conventional liquid developing device disclosed in U.S. Pat. No. 5,255,058. Referring to FIG. 1, an electrostatic latent image is formed on a photosensitive body 10, and an ink supply unit develops the electrostatic latent image by supplying ink to the photosensitive body 10. The developed electrostatic latent image on the photosensitive body 10 is transferred to a transfer body 30, and the transfer body 30 prints the image on a sheet of paper 72.
The ink supply unit prepares the ink having a toner concentration less than 3% solid and supplies the ink between the photosensitive body 10 and a developing roller 38. To this end, the ink supply unit includes concentrated cartridges 82 and 84 in which concentrated ink having a toner concentration of about 25% solid is stored, a solvent cartridge 86 in which a pure solvent is stored, mixing tanks 55, 57, 59, and 61 which mix the concentrated ink with the pure solvent to prepare ink having a uniform concentration of about 2-3% solid, a supplying portion 20 which supplies the ink stored in the mixing tanks 55, 57, 59, and 61 to the developing roller 38 by pumping the ink into pumps 90, 92, 94, and 96, and a drawing portion which draws the ink remaining after the electrostatic latent image is developed. The drawing portion includes a collecting container 50 which collects the ink dropping after being supplied to the developing roller 38 and the photosensitive body 10 and returns the ink to the mixing tanks 55, 57, 59, and 61 for different colors, a squeeze roller 26 which presses the photosensitive body 10 on which the image is developed and squeezes a solvent contained in the developed image, and a separator 66 which draws the squeezed ink from the collecting container 50, separates toner from the ink, and returns the solvent to a solvent tank 65.
In order to perform a development operation using the conventional liquid developing device having the above structure, first, four colors of ink, such as yellow (Y), magenta (M), cyan (C), and black (K), each having the concentration of 2-3% solid, are prepared in the mixing tanks 55, 57, 59, and 61, respectively. In a case of a system for performing a development operation using a single color, such as black-and white, only one color ink is prepared. Here, in order to realize a color image, a system for preparing the four colors of ink has been disclosed. In order to prepare each of the four colors of ink, the ink supply unit supplies the concentration ink and the pure solvent from the concentrated cartridges 82 and 84 and the solvent cartridge 86, respectively, to each of the mixing tanks 55, 57, 59, and 61, so as to manufacture the four colors of ink, each having a corresponding concentration. To this end, a concentration sensor (not shown) is provided to each of the mixing tanks 55, 57, 59, and 61 and measures the concentration of the mixed ink. If the ink is prepared in this manner, the development operation starts performing. First, a charger 14 charges the photosensitive body 10 to a predetermined potential. Then, a laser scanning unit (LSU) 16 radiates light onto the charged photosensitive body 10 to form an electrostatic latent image corresponding to a desired image by a potential difference between a portion of the photosensitive body 10 onto which light is irradiated and a portion of the photosensitive body 10 onto which light is not irradiated. Subsequently, by operating the pumps 90, 92, 94, and 96, the supplying portion 20 supplies the ink stored in the mixing tanks 55, 57, 59, and 61 between the developing roller 38 and the photosensitive body 10 to form the electrostatic latent image. The developed image is transferred to a transfer roller 30, and if the image has only one color, the image in this state is directly printed on the sheet of paper 72. However, if a color image needs to be realized by superimposing a plurality of colors of ink, the above-described charge, exposure, and development operations are repeatedly performed on each of the four colors, such as yellow (Y), magenta (M), cyan (C), and black (K) so that the developed image for each color is superimposed on the transfer roller 30. Last, the color image formed by superimposing the developed image for each color is printed on the sheet of paper 72 that passes between the transfer roller 30 and a pressing roller 71.
However, as described above, the structure of the liquid image developing system which performs the steps of preparing, supplying, and drawing ink, is considerably complicated. In other words, the concentrated ink and solvent are stored and prepared in each of the cartridges 82, 84, and 86, returned to the mixing tanks 55, 57, 59, and 61 and mixed with ink having the low concentration less than 3% solid for development, the electrostatic latent image is developed with the ink, and the solvent contained in the developed image should be squeezed and drawn to have a high-concentration state suitable for printing, causing a large load on the size and/or cost of a device.